1. Field of the Invention
The present invention relates to the preparation of improved high-protein food products from soybeans, in particular, it relates to a process for making the soybean food product more digestable and for removing a substantial amount of the undesirable flavor constituents using lower alcohols.
2. Description of the Prior Art
The use of alcohols as a solvent in the extraction of oil from soybeans is noted in the two volume treatise on "Soybeans and Soybean Products," edited by Markley, Interscience, 1950. In one instance, mentioned by the editor, as being described by Beckel and Smith in Vol. 16 of "Food Industries," 1944, pages 616-644, alcohol with a small proportion of water was used under pressure to extract the oil while avoiding denaturization of the protein.
More recently, in the Moshy U.S. Pat. No. 3,168,406, a process is disclosed wherein alcohol and water are used to treat soybean meal to make the soybean meal bland and odorless. The process includes mixing soybean flour with alcohol to form a slurry such that the pH is adjusted to the isoelectric range of soy proteins, that is about pH 4-6. The slurry is then heated to a temperature range of 175.degree.-212.degree. F. and cooked for preferably sixty minutes. The supernatent liquid is then removed from the soybean flour by any well known process and the resulting filter cake is washed a number of times with water to remove the alcohol. In one example, the filter cake was dried in a vacuum pan dryer at 28 inches of vacuum at 110.degree. F.
In the Kakade U.S. Pat. Nos. 4,079,155 and 4,132,808, which are assigned to the same assignee as the present application, a proteinaceous soybean material is subjected to a lower alcohol vapor in a pressure chamber under superatmospheric pressure. Simultaneously, the alcohol vapors are slowly and continuously removed from the chamber to volatilize certain undesirable flavor constituents, carrying off the flavor constituents with the escaping vapors. Although the process, as disclosed in the Kakade Patents, produces a satisfactory product in terms of a bland and odorless soybean product, a considerable amount of alcohol is used. Specifically, the ratio of alcohol to soybean flour used was 33 pounds of alcohol to 60 pounds of soybean flour or approximately one part of alcohol to every two parts of soybean flour that is treated.